English-to-Japanese translation software entitled “Internet King of Translation” sold in Japan by the assignee of the instant application includes, in addition to a system (basic) dictionary, six dictionaries classified by the fields of “Sports”, “Arts”, “Politics”, “Business”, “Entertainment” and “Internet”, as well as a user dictionary whose translation words may be edited, from time to time, by a user. This software translates English sentences into Japanese sentences by using the translation words in these dictionaries.
Several machine translation systems have been known in which domain dictionaries are automatically switched or changed. For example, the machine translation system disclosed in Japanese Unexamined Patent Publication No. 6-60117 analyzes the sentence structure of an original text, checks whether or not translation words in each sentence exist in the respective domain dictionaries, increments translation word check counters corresponding respectively to the dictionaries in which translation words have existed, and sets selection priority of the domain dictionaries depending on numeric count values of the translation word check counters. Also, in the machine translation system disclosed in Japanese Unexamined Patent Publication No. 10-21222, a condition for translation processing is defined based on document identification information which is determined when a document in a first language is accessed. In one embodiment thereof, a particular domain or field is determined by using an Internet URL as the document identification information, and a domain dictionary corresponding thereto is selected.
In conventional machine translation systems, any word not registered in the dictionaries (hereinafter referred to as “unknown word”) cannot be translated. Therefore, a user must consult, for example, a paper dictionary for an appropriate translation word or equivalent for the unknown word, which would result in inefficient and inconvenient translation word searching.